﻿//
// BigInteger.cs - Big Integer implementation
//
// Authors:
//	Ben Maurer
//	Chew Keong TAN
//	Sebastien Pouliot <sebastien@ximian.com>
//	Pieter Philippaerts <Pieter@mentalis.org>
//
// Copyright (c) 2003 Ben Maurer
// All rights reserved
//
// Copyright (c) 2002 Chew Keong TAN
// All rights reserved.
//
// Copyright (C) 2004, 2007 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using Mono.Math.Generator;
using Mono.Math.Prime;
using Mono.Math.Prime.Generator;
using System;
using System.Security.Cryptography;

namespace Mono.Math
{
#if INSIDE_CORLIB
	internal
#else

    public
#endif
    class BigInteger
    {
        #region Data Storage

        /// <summary>
        /// The Length of this BigInteger
        /// </summary>
        private uint length = 1;

        /// <summary>
        /// The data for this BigInteger
        /// </summary>
        private uint[] data;

        #endregion Data Storage

        #region Constants

        /// <summary>
        /// Default length of a BigInteger in bytes
        /// </summary>
        private const uint DEFAULT_LEN = 20;

        /// <summary>
        ///		Table of primes below 2000.
        /// </summary>
        /// <remarks>
        ///		<para>
        ///		This table was generated using Mathematica 4.1 using the following function:
        ///		</para>
        ///		<para>
        ///			<code>
        ///			PrimeTable [x_] := Prime [Range [1, PrimePi [x]]]
        ///			PrimeTable [6000]
        ///			</code>
        ///		</para>
        /// </remarks>
        internal static readonly uint[] smallPrimes = {
            2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71,
            73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151,
            157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233,
            239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317,
            331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419,
            421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503,
            509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607,
            613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701,
            709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773, 787, 797, 809, 811,
            821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881, 883, 887, 907, 911,
            919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997,

            1009, 1013, 1019, 1021, 1031, 1033, 1039, 1049, 1051, 1061, 1063, 1069, 1087,
            1091, 1093, 1097, 1103, 1109, 1117, 1123, 1129, 1151, 1153, 1163, 1171, 1181,
            1187, 1193, 1201, 1213, 1217, 1223, 1229, 1231, 1237, 1249, 1259, 1277, 1279,
            1283, 1289, 1291, 1297, 1301, 1303, 1307, 1319, 1321, 1327, 1361, 1367, 1373,
            1381, 1399, 1409, 1423, 1427, 1429, 1433, 1439, 1447, 1451, 1453, 1459, 1471,
            1481, 1483, 1487, 1489, 1493, 1499, 1511, 1523, 1531, 1543, 1549, 1553, 1559,
            1567, 1571, 1579, 1583, 1597, 1601, 1607, 1609, 1613, 1619, 1621, 1627, 1637,
            1657, 1663, 1667, 1669, 1693, 1697, 1699, 1709, 1721, 1723, 1733, 1741, 1747,
            1753, 1759, 1777, 1783, 1787, 1789, 1801, 1811, 1823, 1831, 1847, 1861, 1867,
            1871, 1873, 1877, 1879, 1889, 1901, 1907, 1913, 1931, 1933, 1949, 1951, 1973,
            1979, 1987, 1993, 1997, 1999,

            2003, 2011, 2017, 2027, 2029, 2039, 2053, 2063, 2069, 2081, 2083, 2087, 2089,
            2099, 2111, 2113, 2129, 2131, 2137, 2141, 2143, 2153, 2161, 2179, 2203, 2207,
            2213, 2221, 2237, 2239, 2243, 2251, 2267, 2269, 2273, 2281, 2287, 2293, 2297,
            2309, 2311, 2333, 2339, 2341, 2347, 2351, 2357, 2371, 2377, 2381, 2383, 2389,
            2393, 2399, 2411, 2417, 2423, 2437, 2441, 2447, 2459, 2467, 2473, 2477, 2503,
            2521, 2531, 2539, 2543, 2549, 2551, 2557, 2579, 2591, 2593, 2609, 2617, 2621,
            2633, 2647, 2657, 2659, 2663, 2671, 2677, 2683, 2687, 2689, 2693, 2699, 2707,
            2711, 2713, 2719, 2729, 2731, 2741, 2749, 2753, 2767, 2777, 2789, 2791, 2797,
            2801, 2803, 2819, 2833, 2837, 2843, 2851, 2857, 2861, 2879, 2887, 2897, 2903,
            2909, 2917, 2927, 2939, 2953, 2957, 2963, 2969, 2971, 2999,

            3001, 3011, 3019, 3023, 3037, 3041, 3049, 3061, 3067, 3079, 3083, 3089, 3109,
            3119, 3121, 3137, 3163, 3167, 3169, 3181, 3187, 3191, 3203, 3209, 3217, 3221,
            3229, 3251, 3253, 3257, 3259, 3271, 3299, 3301, 3307, 3313, 3319, 3323, 3329,
            3331, 3343, 3347, 3359, 3361, 3371, 3373, 3389, 3391, 3407, 3413, 3433, 3449,
            3457, 3461, 3463, 3467, 3469, 3491, 3499, 3511, 3517, 3527, 3529, 3533, 3539,
            3541, 3547, 3557, 3559, 3571, 3581, 3583, 3593, 3607, 3613, 3617, 3623, 3631,
            3637, 3643, 3659, 3671, 3673, 3677, 3691, 3697, 3701, 3709, 3719, 3727, 3733,
            3739, 3761, 3767, 3769, 3779, 3793, 3797, 3803, 3821, 3823, 3833, 3847, 3851,
            3853, 3863, 3877, 3881, 3889, 3907, 3911, 3917, 3919, 3923, 3929, 3931, 3943,
            3947, 3967, 3989,

            4001, 4003, 4007, 4013, 4019, 4021, 4027, 4049, 4051, 4057, 4073, 4079, 4091,
            4093, 4099, 4111, 4127, 4129, 4133, 4139, 4153, 4157, 4159, 4177, 4201, 4211,
            4217, 4219, 4229, 4231, 4241, 4243, 4253, 4259, 4261, 4271, 4273, 4283, 4289,
            4297, 4327, 4337, 4339, 4349, 4357, 4363, 4373, 4391, 4397, 4409, 4421, 4423,
            4441, 4447, 4451, 4457, 4463, 4481, 4483, 4493, 4507, 4513, 4517, 4519, 4523,
            4547, 4549, 4561, 4567, 4583, 4591, 4597, 4603, 4621, 4637, 4639, 4643, 4649,
            4651, 4657, 4663, 4673, 4679, 4691, 4703, 4721, 4723, 4729, 4733, 4751, 4759,
            4783, 4787, 4789, 4793, 4799, 4801, 4813, 4817, 4831, 4861, 4871, 4877, 4889,
            4903, 4909, 4919, 4931, 4933, 4937, 4943, 4951, 4957, 4967, 4969, 4973, 4987,
            4993, 4999,

            5003, 5009, 5011, 5021, 5023, 5039, 5051, 5059, 5077, 5081, 5087, 5099, 5101,
            5107, 5113, 5119, 5147, 5153, 5167, 5171, 5179, 5189, 5197, 5209, 5227, 5231,
            5233, 5237, 5261, 5273, 5279, 5281, 5297, 5303, 5309, 5323, 5333, 5347, 5351,
            5381, 5387, 5393, 5399, 5407, 5413, 5417, 5419, 5431, 5437, 5441, 5443, 5449,
            5471, 5477, 5479, 5483, 5501, 5503, 5507, 5519, 5521, 5527, 5531, 5557, 5563,
            5569, 5573, 5581, 5591, 5623, 5639, 5641, 5647, 5651, 5653, 5657, 5659, 5669,
            5683, 5689, 5693, 5701, 5711, 5717, 5737, 5741, 5743, 5749, 5779, 5783, 5791,
            5801, 5807, 5813, 5821, 5827, 5839, 5843, 5849, 5851, 5857, 5861, 5867, 5869,
            5879, 5881, 5897, 5903, 5923, 5927, 5939, 5953, 5981, 5987
        };

        public enum Sign : int
        {
            Negative = -1,
            Zero = 0,
            Positive = 1
        };

        #region Exception Messages

        private const string WouldReturnNegVal = "Operation would return a negative value";

        #endregion Exception Messages

        #endregion Constants

        #region Constructors

        public BigInteger()
        {
            data = new uint[DEFAULT_LEN];
            this.length = DEFAULT_LEN;
        }

        public BigInteger(Sign sign, uint len)
        {
            this.data = new uint[len];
            this.length = len;
        }

        public BigInteger(BigInteger bi)
        {
            this.data = (uint[])bi.data.Clone();
            this.length = bi.length;
        }

        public BigInteger(BigInteger bi, uint len)
        {
            this.data = new uint[len];

            for (uint i = 0; i < bi.length; i++)
                this.data[i] = bi.data[i];

            this.length = bi.length;
        }

        #endregion Constructors

        #region Conversions

        public BigInteger(byte[] inData)
        {
            if (inData.Length == 0)
                inData = new byte[1];
            length = (uint)inData.Length >> 2;
            int leftOver = inData.Length & 0x3;

            // length not multiples of 4
            if (leftOver != 0) length++;

            data = new uint[length];

            for (int i = inData.Length - 1, j = 0; i >= 3; i -= 4, j++)
            {
                data[j] = (uint)(
                    (inData[i - 3] << (3 * 8)) |
                    (inData[i - 2] << (2 * 8)) |
                    (inData[i - 1] << (1 * 8)) |
                    (inData[i])
                    );
            }

            switch (leftOver)
            {
                case 1: data[length - 1] = (uint)inData[0]; break;
                case 2: data[length - 1] = (uint)((inData[0] << 8) | inData[1]); break;
                case 3: data[length - 1] = (uint)((inData[0] << 16) | (inData[1] << 8) | inData[2]); break;
            }

            this.Normalize();
        }

        public BigInteger(uint[] inData)
        {
            if (inData.Length == 0)
                inData = new uint[1];
            length = (uint)inData.Length;

            data = new uint[length];

            for (int i = (int)length - 1, j = 0; i >= 0; i--, j++)
                data[j] = inData[i];

            this.Normalize();
        }

        public BigInteger(uint ui)
        {
            data = new uint[] { ui };
        }

        public BigInteger(ulong ul)
        {
            data = new uint[2] { (uint)ul, (uint)(ul >> 32) };
            length = 2;

            this.Normalize();
        }

        public static implicit operator BigInteger(uint value)
        {
            return (new BigInteger(value));
        }

        public static implicit operator BigInteger(int value)
        {
            if (value < 0) throw new ArgumentOutOfRangeException("value");
            return (new BigInteger((uint)value));
        }

        public static implicit operator BigInteger(ulong value)
        {
            return (new BigInteger(value));
        }

        /* This is the BigInteger.Parse method I use. This method works
		because BigInteger.ToString returns the input I gave to Parse. */

        public static BigInteger Parse(string number)
        {
            if (number == null)
                throw new ArgumentNullException("number");

            int i = 0, len = number.Length;
            char c;
            bool digits_seen = false;
            BigInteger val = new BigInteger(0);
            if (number[i] == '+')
            {
                i++;
            }
            else if (number[i] == '-')
            {
                throw new FormatException(WouldReturnNegVal);
            }

            for (; i < len; i++)
            {
                c = number[i];
                if (c == '\0')
                {
                    i = len;
                    continue;
                }
                if (c >= '0' && c <= '9')
                {
                    val = val * 10 + (c - '0');
                    digits_seen = true;
                }
                else
                {
                    if (Char.IsWhiteSpace(c))
                    {
                        for (i++; i < len; i++)
                        {
                            if (!Char.IsWhiteSpace(number[i]))
                                throw new FormatException();
                        }
                        break;
                    }
                    else
                        throw new FormatException();
                }
            }
            if (!digits_seen)
                throw new FormatException();
            return val;
        }

        #endregion Conversions

        #region Operators

        public static BigInteger operator +(BigInteger bi1, BigInteger bi2)
        {
            if (bi1 == 0)
                return new BigInteger(bi2);
            else if (bi2 == 0)
                return new BigInteger(bi1);
            else
                return Kernel.AddSameSign(bi1, bi2);
        }

        public static BigInteger operator -(BigInteger bi1, BigInteger bi2)
        {
            if (bi2 == 0)
                return new BigInteger(bi1);

            if (bi1 == 0)
                throw new ArithmeticException(WouldReturnNegVal);

            switch (Kernel.Compare(bi1, bi2))
            {
                case Sign.Zero:
                    return 0;

                case Sign.Positive:
                    return Kernel.Subtract(bi1, bi2);

                case Sign.Negative:
                    throw new ArithmeticException(WouldReturnNegVal);
                default:
                    throw new Exception();
            }
        }

        public static int operator %(BigInteger bi, int i)
        {
            if (i > 0)
                return (int)Kernel.DwordMod(bi, (uint)i);
            else
                return -(int)Kernel.DwordMod(bi, (uint)-i);
        }

        public static uint operator %(BigInteger bi, uint ui)
        {
            return Kernel.DwordMod(bi, (uint)ui);
        }

        public static BigInteger operator %(BigInteger bi1, BigInteger bi2)
        {
            return Kernel.multiByteDivide(bi1, bi2)[1];
        }

        public static BigInteger operator /(BigInteger bi, int i)
        {
            if (i > 0)
                return Kernel.DwordDiv(bi, (uint)i);

            throw new ArithmeticException(WouldReturnNegVal);
        }

        public static BigInteger operator /(BigInteger bi1, BigInteger bi2)
        {
            return Kernel.multiByteDivide(bi1, bi2)[0];
        }

        public static BigInteger operator *(BigInteger bi1, BigInteger bi2)
        {
            if (bi1 == 0 || bi2 == 0) return 0;

            //
            // Validate pointers
            //
            if (bi1.data.Length < bi1.length) throw new IndexOutOfRangeException("bi1 out of range");
            if (bi2.data.Length < bi2.length) throw new IndexOutOfRangeException("bi2 out of range");

            BigInteger ret = new BigInteger(Sign.Positive, bi1.length + bi2.length);

            Kernel.Multiply(bi1.data, 0, bi1.length, bi2.data, 0, bi2.length, ret.data, 0);

            ret.Normalize();
            return ret;
        }

        public static BigInteger operator *(BigInteger bi, int i)
        {
            if (i < 0) throw new ArithmeticException(WouldReturnNegVal);
            if (i == 0) return 0;
            if (i == 1) return new BigInteger(bi);

            return Kernel.MultiplyByDword(bi, (uint)i);
        }

        public static BigInteger operator <<(BigInteger bi1, int shiftVal)
        {
            return Kernel.LeftShift(bi1, shiftVal);
        }

        public static BigInteger operator >>(BigInteger bi1, int shiftVal)
        {
            return Kernel.RightShift(bi1, shiftVal);
        }

        #endregion Operators

        #region Friendly names for operators

        // with names suggested by FxCop 1.30

        public static BigInteger Add(BigInteger bi1, BigInteger bi2)
        {
            return (bi1 + bi2);
        }

        public static BigInteger Subtract(BigInteger bi1, BigInteger bi2)
        {
            return (bi1 - bi2);
        }

        public static int Modulus(BigInteger bi, int i)
        {
            return (bi % i);
        }

        public static uint Modulus(BigInteger bi, uint ui)
        {
            return (bi % ui);
        }

        public static BigInteger Modulus(BigInteger bi1, BigInteger bi2)
        {
            return (bi1 % bi2);
        }

        public static BigInteger Divid(BigInteger bi, int i)
        {
            return (bi / i);
        }

        public static BigInteger Divid(BigInteger bi1, BigInteger bi2)
        {
            return (bi1 / bi2);
        }

        public static BigInteger Multiply(BigInteger bi1, BigInteger bi2)
        {
            return (bi1 * bi2);
        }

        public static BigInteger Multiply(BigInteger bi, int i)
        {
            return (bi * i);
        }

        #endregion Friendly names for operators

        #region Random

        private static RandomNumberGenerator rng;

        private static RandomNumberGenerator Rng
        {
            get
            {
                if (rng == null)
                    rng = RandomNumberGenerator.Create();
                return rng;
            }
        }

        /// <summary>
        /// Generates a new, random BigInteger of the specified length.
        /// </summary>
        /// <param name="bits">The number of bits for the new number.</param>
        /// <param name="rng">A random number generator to use to obtain the bits.</param>
        /// <returns>A random number of the specified length.</returns>
        public static BigInteger GenerateRandom(int bits, RandomNumberGenerator rng)
        {
            int dwords = bits >> 5;
            int remBits = bits & 0x1F;

            if (remBits != 0)
                dwords++;

            BigInteger ret = new BigInteger(Sign.Positive, (uint)dwords + 1);
            byte[] random = new byte[dwords << 2];

            rng.GetBytes(random);
            Buffer.BlockCopy(random, 0, ret.data, 0, (int)dwords << 2);

            if (remBits != 0)
            {
                uint mask = (uint)(0x01 << (remBits - 1));
                ret.data[dwords - 1] |= mask;

                mask = (uint)(0xFFFFFFFF >> (32 - remBits));
                ret.data[dwords - 1] &= mask;
            }
            else
                ret.data[dwords - 1] |= 0x80000000;

            ret.Normalize();
            return ret;
        }

        /// <summary>
        /// Generates a new, random BigInteger of the specified length using the default RNG crypto service provider.
        /// </summary>
        /// <param name="bits">The number of bits for the new number.</param>
        /// <returns>A random number of the specified length.</returns>
        public static BigInteger GenerateRandom(int bits)
        {
            return GenerateRandom(bits, Rng);
        }

        /// <summary>
        /// Randomizes the bits in "this" from the specified RNG.
        /// </summary>
        /// <param name="rng">A RNG.</param>
        public void Randomize(RandomNumberGenerator rng)
        {
            if (this == 0)
                return;

            int bits = this.BitCount();
            int dwords = bits >> 5;
            int remBits = bits & 0x1F;

            if (remBits != 0)
                dwords++;

            byte[] random = new byte[dwords << 2];

            rng.GetBytes(random);
            Buffer.BlockCopy(random, 0, data, 0, (int)dwords << 2);

            if (remBits != 0)
            {
                uint mask = (uint)(0x01 << (remBits - 1));
                data[dwords - 1] |= mask;

                mask = (uint)(0xFFFFFFFF >> (32 - remBits));
                data[dwords - 1] &= mask;
            }
            else
                data[dwords - 1] |= 0x80000000;

            Normalize();
        }

        /// <summary>
        /// Randomizes the bits in "this" from the default RNG.
        /// </summary>
        public void Randomize()
        {
            Randomize(Rng);
        }

        #endregion Random

        #region Bitwise

        public int BitCount()
        {
            this.Normalize();

            uint value = data[length - 1];
            uint mask = 0x80000000;
            uint bits = 32;

            while (bits > 0 && (value & mask) == 0)
            {
                bits--;
                mask >>= 1;
            }
            bits += ((length - 1) << 5);

            return (int)bits;
        }

        /// <summary>
        /// Tests if the specified bit is 1.
        /// </summary>
        /// <param name="bitNum">The bit to test. The least significant bit is 0.</param>
        /// <returns>True if bitNum is set to 1, else false.</returns>
        public bool TestBit(uint bitNum)
        {
            uint bytePos = bitNum >> 5;             // divide by 32
            byte bitPos = (byte)(bitNum & 0x1F);    // get the lowest 5 bits

            uint mask = (uint)1 << bitPos;
            return ((this.data[bytePos] & mask) != 0);
        }

        public bool TestBit(int bitNum)
        {
            if (bitNum < 0) throw new IndexOutOfRangeException("bitNum out of range");

            uint bytePos = (uint)bitNum >> 5;             // divide by 32
            byte bitPos = (byte)(bitNum & 0x1F);    // get the lowest 5 bits

            uint mask = (uint)1 << bitPos;
            return ((this.data[bytePos] | mask) == this.data[bytePos]);
        }

        public void SetBit(uint bitNum)
        {
            SetBit(bitNum, true);
        }

        public void ClearBit(uint bitNum)
        {
            SetBit(bitNum, false);
        }

        public void SetBit(uint bitNum, bool value)
        {
            uint bytePos = bitNum >> 5;             // divide by 32

            if (bytePos < this.length)
            {
                uint mask = (uint)1 << (int)(bitNum & 0x1F);
                if (value)
                    this.data[bytePos] |= mask;
                else
                    this.data[bytePos] &= ~mask;
            }
        }

        public int LowestSetBit()
        {
            if (this == 0) return -1;
            int i = 0;
            while (!TestBit(i)) i++;
            return i;
        }

        public byte[] GetBytes()
        {
            if (this == 0) return new byte[1];

            int numBits = BitCount();
            int numBytes = numBits >> 3;
            if ((numBits & 0x7) != 0)
                numBytes++;

            byte[] result = new byte[numBytes];

            int numBytesInWord = numBytes & 0x3;
            if (numBytesInWord == 0) numBytesInWord = 4;

            int pos = 0;
            for (int i = (int)length - 1; i >= 0; i--)
            {
                uint val = data[i];
                for (int j = numBytesInWord - 1; j >= 0; j--)
                {
                    result[pos + j] = (byte)(val & 0xFF);
                    val >>= 8;
                }
                pos += numBytesInWord;
                numBytesInWord = 4;
            }
            return result;
        }

        #endregion Bitwise

        #region Compare

        public static bool operator ==(BigInteger bi1, uint ui)
        {
            if (bi1.length != 1) bi1.Normalize();
            return bi1.length == 1 && bi1.data[0] == ui;
        }

        public static bool operator !=(BigInteger bi1, uint ui)
        {
            if (bi1.length != 1) bi1.Normalize();
            return !(bi1.length == 1 && bi1.data[0] == ui);
        }

        public static bool operator ==(BigInteger bi1, BigInteger bi2)
        {
            // we need to compare with null
            if ((bi1 as object) == (bi2 as object))
                return true;
            if (null == bi1 || null == bi2)
                return false;
            return Kernel.Compare(bi1, bi2) == 0;
        }

        public static bool operator !=(BigInteger bi1, BigInteger bi2)
        {
            // we need to compare with null
            if ((bi1 as object) == (bi2 as object))
                return false;
            if (null == bi1 || null == bi2)
                return true;
            return Kernel.Compare(bi1, bi2) != 0;
        }

        public static bool operator >(BigInteger bi1, BigInteger bi2)
        {
            return Kernel.Compare(bi1, bi2) > 0;
        }

        public static bool operator <(BigInteger bi1, BigInteger bi2)
        {
            return Kernel.Compare(bi1, bi2) < 0;
        }

        public static bool operator >=(BigInteger bi1, BigInteger bi2)
        {
            return Kernel.Compare(bi1, bi2) >= 0;
        }

        public static bool operator <=(BigInteger bi1, BigInteger bi2)
        {
            return Kernel.Compare(bi1, bi2) <= 0;
        }

        public Sign Compare(BigInteger bi)
        {
            return Kernel.Compare(this, bi);
        }

        #endregion Compare

        #region Formatting

        public string ToString(uint radix)
        {
            return ToString(radix, "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ");
        }

        public string ToString(uint radix, string characterSet)
        {
            if (characterSet.Length < radix)
                throw new ArgumentException("charSet length less than radix", "characterSet");
            if (radix == 1)
                throw new ArgumentException("There is no such thing as radix one notation", "radix");

            if (this == 0) return "0";
            if (this == 1) return "1";

            string result = "";

            BigInteger a = new BigInteger(this);

            while (a != 0)
            {
                uint rem = Kernel.SingleByteDivideInPlace(a, radix);
                result = characterSet[(int)rem] + result;
            }

            return result;
        }

        #endregion Formatting

        #region Misc

        /// <summary>
        ///     Normalizes this by setting the length to the actual number of
        ///     uints used in data and by setting the sign to Sign.Zero if the
        ///     value of this is 0.
        /// </summary>
        private void Normalize()
        {
            // Normalize length
            while (length > 0 && data[length - 1] == 0) length--;

            // Check for zero
            if (length == 0)
                length++;
        }

        public void Clear()
        {
            for (int i = 0; i < length; i++)
                data[i] = 0x00;
        }

        #endregion Misc

        #region Object Impl

        public override int GetHashCode()
        {
            uint val = 0;

            for (uint i = 0; i < this.length; i++)
                val ^= this.data[i];

            return (int)val;
        }

        public override string ToString()
        {
            return ToString(10);
        }

        public override bool Equals(object o)
        {
            if (o == null)
                return false;
            if (o is int)
                return (int)o >= 0 && this == (uint)o;

            BigInteger bi = o as BigInteger;
            if (bi == null)
                return false;

            return Kernel.Compare(this, bi) == 0;
        }

        #endregion Object Impl

        #region Number Theory

        public BigInteger GCD(BigInteger bi)
        {
            return Kernel.gcd(this, bi);
        }

        public BigInteger ModInverse(BigInteger modulus)
        {
            return Kernel.modInverse(this, modulus);
        }

        public BigInteger ModPow(BigInteger exp, BigInteger n)
        {
            ModulusRing mr = new ModulusRing(n);
            return mr.Pow(this, exp);
        }

        #endregion Number Theory

        #region Prime Testing

        public bool IsProbablePrime()
        {
            // can we use our small-prime table ?
            if (this <= smallPrimes[smallPrimes.Length - 1])
            {
                for (int p = 0; p < smallPrimes.Length; p++)
                {
                    if (this == smallPrimes[p])
                        return true;
                }
                // the list is complete, so it's not a prime
                return false;
            }

            // otherwise check if we can divide by one of the small primes
            for (int p = 0; p < smallPrimes.Length; p++)
            {
                if (this % smallPrimes[p] == 0)
                    return false;
            }
            // the last step is to confirm the "large" prime with the SPP or Miller-Rabin test
            return PrimalityTests.Test(this, Prime.ConfidenceFactor.Medium);
        }

        #endregion Prime Testing

        #region Prime Number Generation

        /// <summary>
        /// Generates the smallest prime >= bi
        /// </summary>
        /// <param name="bi">A BigInteger</param>
        /// <returns>The smallest prime >= bi. More mathematically, if bi is prime: bi, else Prime [PrimePi [bi] + 1].</returns>
        public static BigInteger NextHighestPrime(BigInteger bi)
        {
            NextPrimeFinder npf = new NextPrimeFinder();
            return npf.GenerateNewPrime(0, bi);
        }

        public static BigInteger GeneratePseudoPrime(int bits)
        {
            SequentialSearchPrimeGeneratorBase sspg = new SequentialSearchPrimeGeneratorBase();
            return sspg.GenerateNewPrime(bits);
        }

        /// <summary>
        /// Increments this by two
        /// </summary>
        public void Incr2()
        {
            int i = 0;

            data[0] += 2;

            // If there was no carry, nothing to do
            if (data[0] < 2)
            {
                // Account for the first carry
                data[++i]++;

                // Keep adding until no carry
                while (data[i++] == 0x0)
                    data[i]++;

                // See if we increased the data length
                if (length == (uint)i)
                    length++;
            }
        }

        #endregion Prime Number Generation

#if INSIDE_CORLIB
		internal
#else

        public
#endif
        sealed class ModulusRing
        {
            private BigInteger mod, constant;

            public ModulusRing(BigInteger modulus)
            {
                this.mod = modulus;

                // calculate constant = b^ (2k) / m
                uint i = mod.length << 1;

                constant = new BigInteger(Sign.Positive, i + 1);
                constant.data[i] = 0x00000001;

                constant = constant / mod;
            }

            public void BarrettReduction(BigInteger x)
            {
                BigInteger n = mod;
                uint k = n.length,
                    kPlusOne = k + 1,
                    kMinusOne = k - 1;

                // x < mod, so nothing to do.
                if (x.length < k) return;

                BigInteger q3;

                //
                // Validate pointers
                //
                if (x.data.Length < x.length) throw new IndexOutOfRangeException("x out of range");

                // q1 = x / b^ (k-1)
                // q2 = q1 * constant
                // q3 = q2 / b^ (k+1), Needs to be accessed with an offset of kPlusOne

                // TODO: We should the method in HAC p 604 to do this (14.45)
                q3 = new BigInteger(Sign.Positive, x.length - kMinusOne + constant.length);
                Kernel.Multiply(x.data, kMinusOne, x.length - kMinusOne, constant.data, 0, constant.length, q3.data, 0);

                // r1 = x mod b^ (k+1)
                // i.e. keep the lowest (k+1) words

                uint lengthToCopy = (x.length > kPlusOne) ? kPlusOne : x.length;

                x.length = lengthToCopy;
                x.Normalize();

                // r2 = (q3 * n) mod b^ (k+1)
                // partial multiplication of q3 and n

                BigInteger r2 = new BigInteger(Sign.Positive, kPlusOne);
                Kernel.MultiplyMod2p32pmod(q3.data, (int)kPlusOne, (int)q3.length - (int)kPlusOne, n.data, 0, (int)n.length, r2.data, 0, (int)kPlusOne);

                r2.Normalize();

                if (r2 <= x)
                {
                    Kernel.MinusEq(x, r2);
                }
                else
                {
                    BigInteger val = new BigInteger(Sign.Positive, kPlusOne + 1);
                    val.data[kPlusOne] = 0x00000001;

                    Kernel.MinusEq(val, r2);
                    Kernel.PlusEq(x, val);
                }

                while (x >= n)
                    Kernel.MinusEq(x, n);
            }

            public BigInteger Multiply(BigInteger a, BigInteger b)
            {
                if (a == 0 || b == 0) return 0;

                if (a > mod)
                    a %= mod;

                if (b > mod)
                    b %= mod;

                BigInteger ret = a * b;
                BarrettReduction(ret);

                return ret;
            }

            public BigInteger Difference(BigInteger a, BigInteger b)
            {
                Sign cmp = Kernel.Compare(a, b);
                BigInteger diff;

                switch (cmp)
                {
                    case Sign.Zero:
                        return 0;

                    case Sign.Positive:
                        diff = a - b; break;
                    case Sign.Negative:
                        diff = b - a; break;
                    default:
                        throw new Exception();
                }

                if (diff >= mod)
                {
                    if (diff.length >= mod.length << 1)
                        diff %= mod;
                    else
                        BarrettReduction(diff);
                }
                if (cmp == Sign.Negative)
                    diff = mod - diff;
                return diff;
            }

#if true

            public BigInteger Pow(BigInteger a, BigInteger k)
            {
                BigInteger b = new BigInteger(1);
                if (k == 0)
                    return b;

                BigInteger A = a;
                if (k.TestBit(0))
                    b = a;

                for (int i = 1; i < k.BitCount(); i++)
                {
                    A = Multiply(A, A);
                    if (k.TestBit(i))
                        b = Multiply(A, b);
                }
                return b;
            }

#else
			public BigInteger Pow (BigInteger b, BigInteger exp)
			{
				if ((mod.data [0] & 1) == 1) return OddPow (b, exp);
				else return EvenPow (b, exp);
			}

			public BigInteger EvenPow (BigInteger b, BigInteger exp)
			{
				BigInteger resultNum = new BigInteger ((BigInteger)1, mod.length << 1);
				BigInteger tempNum = new BigInteger (b % mod, mod.length << 1);  // ensures (tempNum * tempNum) < b^ (2k)

				uint totalBits = (uint)exp.BitCount ();

				uint [] wkspace = new uint [mod.length << 1];

				// perform squaring and multiply exponentiation
				for (uint pos = 0; pos < totalBits; pos++) {
					if (exp.TestBit (pos)) {
						Array.Clear (wkspace, 0, wkspace.Length);
						Kernel.Multiply (resultNum.data, 0, resultNum.length, tempNum.data, 0, tempNum.length, wkspace, 0);
						resultNum.length += tempNum.length;
						uint [] t = wkspace;
						wkspace = resultNum.data;
						resultNum.data = t;

						BarrettReduction (resultNum);
					}

					Kernel.SquarePositive (tempNum, ref wkspace);
					BarrettReduction (tempNum);

					if (tempNum == 1) {
						return resultNum;
					}
				}

				return resultNum;
			}

			private BigInteger OddPow (BigInteger b, BigInteger exp)
			{
				BigInteger resultNum = new BigInteger (Montgomery.ToMont (1, mod), mod.length << 1);
				BigInteger tempNum = new BigInteger (Montgomery.ToMont (b, mod), mod.length << 1);  // ensures (tempNum * tempNum) < b^ (2k)
				uint mPrime = Montgomery.Inverse (mod.data [0]);
				uint totalBits = (uint)exp.BitCount ();

				uint [] wkspace = new uint [mod.length << 1];

				// perform squaring and multiply exponentiation
				for (uint pos = 0; pos < totalBits; pos++) {
					if (exp.TestBit (pos)) {
						Array.Clear (wkspace, 0, wkspace.Length);
						Kernel.Multiply (resultNum.data, 0, resultNum.length, tempNum.data, 0, tempNum.length, wkspace, 0);
						resultNum.length += tempNum.length;
						uint [] t = wkspace;
						wkspace = resultNum.data;
						resultNum.data = t;

						Montgomery.Reduce (resultNum, mod, mPrime);
					}

					// the value of tempNum is required in the last loop
					if (pos < totalBits - 1) {
						Kernel.SquarePositive (tempNum, ref wkspace);
						Montgomery.Reduce (tempNum, mod, mPrime);
					}
				}

				Montgomery.Reduce (resultNum, mod, mPrime);
				return resultNum;
			}
#endif

            #region Pow Small Base

            // TODO: Make tests for this, not really needed b/c prime stuff
            // checks it, but still would be nice
#if true

            public BigInteger Pow(uint b, BigInteger exp)
            {
                return Pow(new BigInteger(b), exp);
            }

#else
			public BigInteger Pow (uint b, BigInteger exp)
			{
//				if (b != 2) {
					if ((mod.data [0] & 1) == 1)
						return OddPow (b, exp);
					else
						return EvenPow (b, exp);
/* buggy in some cases (like the well tested primes)
				} else {
					if ((mod.data [0] & 1) == 1)
						return OddModTwoPow (exp);
					else
						return EvenModTwoPow (exp);
				}*/
			}

			private unsafe BigInteger OddPow (uint b, BigInteger exp)
			{
				exp.Normalize ();
				uint [] wkspace = new uint [mod.length << 1 + 1];

				BigInteger resultNum = Montgomery.ToMont ((BigInteger)b, this.mod);
				resultNum = new BigInteger (resultNum, mod.length << 1 +1);

				uint mPrime = Montgomery.Inverse (mod.data [0]);

				int bc = exp.BitCount () - 2;
				uint pos = (bc > 1 ? (uint) bc : 1);

				//
				// We know that the first itr will make the val b
				//

				do {
					//
					// r = r ^ 2 % m
					//
					Kernel.SquarePositive (resultNum, ref wkspace);
					resultNum = Montgomery.Reduce (resultNum, mod, mPrime);

					if (exp.TestBit (pos)) {
						//
						// r = r * b % m
						//

						// TODO: Is Unsafe really speeding things up?
						fixed (uint* u = resultNum.data) {
							uint i = 0;
							ulong mc = 0;

							do {
								mc += (ulong)u [i] * (ulong)b;
								u [i] = (uint)mc;
								mc >>= 32;
							} while (++i < resultNum.length);

							if (resultNum.length < mod.length) {
								if (mc != 0) {
									u [i] = (uint)mc;
									resultNum.length++;
									while (resultNum >= mod)
										Kernel.MinusEq (resultNum, mod);
								}
							} else if (mc != 0) {
								//
								// First, we estimate the quotient by dividing
								// the first part of each of the numbers. Then
								// we correct this, if necessary, with a subtraction.
								//

								uint cc = (uint)mc;

								// We would rather have this estimate overshoot,
								// so we add one to the divisor
								uint divEstimate;
								if (mod.data [mod.length - 1] < UInt32.MaxValue) {
									divEstimate = (uint) ((((ulong)cc << 32) | (ulong) u [i -1]) /
										(mod.data [mod.length-1] + 1));
								}
								else {
									// guess but don't divide by 0
									divEstimate = (uint) ((((ulong)cc << 32) | (ulong) u [i -1]) /
										(mod.data [mod.length-1]));
								}

								uint t;

								i = 0;
								mc = 0;
								do {
									mc += (ulong)mod.data [i] * (ulong)divEstimate;
									t = u [i];
									u [i] -= (uint)mc;
									mc >>= 32;
									if (u [i] > t) mc++;
									i++;
								} while (i < resultNum.length);
								cc -= (uint)mc;

								if (cc != 0) {
									uint sc = 0, j = 0;
									uint [] s = mod.data;
									do {
										uint a = s [j];
										if (((a += sc) < sc) | ((u [j] -= a) > ~a)) sc = 1;
										else sc = 0;
										j++;
									} while (j < resultNum.length);
									cc -= sc;
								}
								while (resultNum >= mod)
									Kernel.MinusEq (resultNum, mod);
							} else {
								while (resultNum >= mod)
									Kernel.MinusEq (resultNum, mod);
							}
						}
					}
				} while (pos-- > 0);

				resultNum = Montgomery.Reduce (resultNum, mod, mPrime);
				return resultNum;
			}

			private unsafe BigInteger EvenPow (uint b, BigInteger exp)
			{
				exp.Normalize ();
				uint [] wkspace = new uint [mod.length << 1 + 1];
				BigInteger resultNum = new BigInteger ((BigInteger)b, mod.length << 1 + 1);

				uint pos = (uint)exp.BitCount () - 2;

				//
				// We know that the first itr will make the val b
				//

				do {
					//
					// r = r ^ 2 % m
					//
					Kernel.SquarePositive (resultNum, ref wkspace);
					if (!(resultNum.length < mod.length))
						BarrettReduction (resultNum);

					if (exp.TestBit (pos)) {
						//
						// r = r * b % m
						//

						// TODO: Is Unsafe really speeding things up?
						fixed (uint* u = resultNum.data) {
							uint i = 0;
							ulong mc = 0;

							do {
								mc += (ulong)u [i] * (ulong)b;
								u [i] = (uint)mc;
								mc >>= 32;
							} while (++i < resultNum.length);

							if (resultNum.length < mod.length) {
								if (mc != 0) {
									u [i] = (uint)mc;
									resultNum.length++;
									while (resultNum >= mod)
										Kernel.MinusEq (resultNum, mod);
								}
							} else if (mc != 0) {
								//
								// First, we estimate the quotient by dividing
								// the first part of each of the numbers. Then
								// we correct this, if necessary, with a subtraction.
								//

								uint cc = (uint)mc;

								// We would rather have this estimate overshoot,
								// so we add one to the divisor
								uint divEstimate = (uint) ((((ulong)cc << 32) | (ulong) u [i -1]) /
									(mod.data [mod.length-1] + 1));

								uint t;

								i = 0;
								mc = 0;
								do {
									mc += (ulong)mod.data [i] * (ulong)divEstimate;
									t = u [i];
									u [i] -= (uint)mc;
									mc >>= 32;
									if (u [i] > t) mc++;
									i++;
								} while (i < resultNum.length);
								cc -= (uint)mc;

								if (cc != 0) {
									uint sc = 0, j = 0;
									uint [] s = mod.data;
									do {
										uint a = s [j];
										if (((a += sc) < sc) | ((u [j] -= a) > ~a)) sc = 1;
										else sc = 0;
										j++;
									} while (j < resultNum.length);
									cc -= sc;
								}
								while (resultNum >= mod)
									Kernel.MinusEq (resultNum, mod);
							} else {
								while (resultNum >= mod)
									Kernel.MinusEq (resultNum, mod);
							}
						}
					}
				} while (pos-- > 0);

				return resultNum;
			}
#endif
            /* known to be buggy in some cases */
#if false
			private unsafe BigInteger EvenModTwoPow (BigInteger exp)
			{
				exp.Normalize ();
				uint [] wkspace = new uint [mod.length << 1 + 1];

				BigInteger resultNum = new BigInteger (2, mod.length << 1 +1);

				uint value = exp.data [exp.length - 1];
				uint mask = 0x80000000;

				// Find the first bit of the exponent
				while ((value & mask) == 0)
					mask >>= 1;

				//
				// We know that the first itr will make the val 2,
				// so eat one bit of the exponent
				//
				mask >>= 1;

				uint wPos = exp.length - 1;

				do {
					value = exp.data [wPos];
					do {
						Kernel.SquarePositive (resultNum, ref wkspace);
						if (resultNum.length >= mod.length)
							BarrettReduction (resultNum);

						if ((value & mask) != 0) {
							//
							// resultNum = (resultNum * 2) % mod
							//

							fixed (uint* u = resultNum.data) {
								//
								// Double
								//
								uint* uu = u;
								uint* uuE = u + resultNum.length;
								uint x, carry = 0;
								while (uu < uuE) {
									x = *uu;
									*uu = (x << 1) | carry;
									carry = x >> (32 - 1);
									uu++;
								}

								// subtraction inlined because we know it is square
								if (carry != 0 || resultNum >= mod) {
									uu = u;
									uint c = 0;
									uint [] s = mod.data;
									uint i = 0;
									do {
										uint a = s [i];
										if (((a += c) < c) | ((* (uu++) -= a) > ~a))
											c = 1;
										else
											c = 0;
										i++;
									} while (uu < uuE);
								}
							}
						}
					} while ((mask >>= 1) > 0);
					mask = 0x80000000;
				} while (wPos-- > 0);

				return resultNum;
			}

			private unsafe BigInteger OddModTwoPow (BigInteger exp)
			{
				uint [] wkspace = new uint [mod.length << 1 + 1];

				BigInteger resultNum = Montgomery.ToMont ((BigInteger)2, this.mod);
				resultNum = new BigInteger (resultNum, mod.length << 1 +1);

				uint mPrime = Montgomery.Inverse (mod.data [0]);

				//
				// TODO: eat small bits, the ones we can do with no modular reduction
				//
				uint pos = (uint)exp.BitCount () - 2;

				do {
					Kernel.SquarePositive (resultNum, ref wkspace);
					resultNum = Montgomery.Reduce (resultNum, mod, mPrime);

					if (exp.TestBit (pos)) {
						//
						// resultNum = (resultNum * 2) % mod
						//

						fixed (uint* u = resultNum.data) {
							//
							// Double
							//
							uint* uu = u;
							uint* uuE = u + resultNum.length;
							uint x, carry = 0;
							while (uu < uuE) {
								x = *uu;
								*uu = (x << 1) | carry;
								carry = x >> (32 - 1);
								uu++;
							}

							// subtraction inlined because we know it is square
							if (carry != 0 || resultNum >= mod) {
								fixed (uint* s = mod.data) {
									uu = u;
									uint c = 0;
									uint* ss = s;
									do {
										uint a = *ss++;
										if (((a += c) < c) | ((* (uu++) -= a) > ~a))
											c = 1;
										else
											c = 0;
									} while (uu < uuE);
								}
							}
						}
					}
				} while (pos-- > 0);

				resultNum = Montgomery.Reduce (resultNum, mod, mPrime);
				return resultNum;
			}
#endif

            #endregion Pow Small Base
        }

        /// <summary>
        /// Low level functions for the BigInteger
        /// </summary>
        private sealed class Kernel
        {
            #region Addition/Subtraction

            /// <summary>
            /// Adds two numbers with the same sign.
            /// </summary>
            /// <param name="bi1">A BigInteger</param>
            /// <param name="bi2">A BigInteger</param>
            /// <returns>bi1 + bi2</returns>
            public static BigInteger AddSameSign(BigInteger bi1, BigInteger bi2)
            {
                uint[] x, y;
                uint yMax, xMax, i = 0;

                // x should be bigger
                if (bi1.length < bi2.length)
                {
                    x = bi2.data;
                    xMax = bi2.length;
                    y = bi1.data;
                    yMax = bi1.length;
                }
                else
                {
                    x = bi1.data;
                    xMax = bi1.length;
                    y = bi2.data;
                    yMax = bi2.length;
                }

                BigInteger result = new BigInteger(Sign.Positive, xMax + 1);

                uint[] r = result.data;

                ulong sum = 0;

                // Add common parts of both numbers
                do
                {
                    sum = ((ulong)x[i]) + ((ulong)y[i]) + sum;
                    r[i] = (uint)sum;
                    sum >>= 32;
                } while (++i < yMax);

                // Copy remainder of longer number while carry propagation is required
                bool carry = (sum != 0);

                if (carry)
                {
                    if (i < xMax)
                    {
                        do
                            carry = ((r[i] = x[i] + 1) == 0);
                        while (++i < xMax && carry);
                    }

                    if (carry)
                    {
                        r[i] = 1;
                        result.length = ++i;
                        return result;
                    }
                }

                // Copy the rest
                if (i < xMax)
                {
                    do
                        r[i] = x[i];
                    while (++i < xMax);
                }

                result.Normalize();
                return result;
            }

            public static BigInteger Subtract(BigInteger big, BigInteger small)
            {
                BigInteger result = new BigInteger(Sign.Positive, big.length);

                uint[] r = result.data, b = big.data, s = small.data;
                uint i = 0, c = 0;

                do
                {
                    uint x = s[i];
                    if (((x += c) < c) | ((r[i] = b[i] - x) > ~x))
                        c = 1;
                    else
                        c = 0;
                } while (++i < small.length);

                if (i == big.length) goto fixup;

                if (c == 1)
                {
                    do
                        r[i] = b[i] - 1;
                    while (b[i++] == 0 && i < big.length);

                    if (i == big.length) goto fixup;
                }

                do
                    r[i] = b[i];
                while (++i < big.length);

            fixup:

                result.Normalize();
                return result;
            }

            public static void MinusEq(BigInteger big, BigInteger small)
            {
                uint[] b = big.data, s = small.data;
                uint i = 0, c = 0;

                do
                {
                    uint x = s[i];
                    if (((x += c) < c) | ((b[i] -= x) > ~x))
                        c = 1;
                    else
                        c = 0;
                } while (++i < small.length);

                if (i == big.length) goto fixup;

                if (c == 1)
                {
                    do
                        b[i]--;
                    while (b[i++] == 0 && i < big.length);
                }

            fixup:

                // Normalize length
                while (big.length > 0 && big.data[big.length - 1] == 0) big.length--;

                // Check for zero
                if (big.length == 0)
                    big.length++;
            }

            public static void PlusEq(BigInteger bi1, BigInteger bi2)
            {
                uint[] x, y;
                uint yMax, xMax, i = 0;
                bool flag = false;

                // x should be bigger
                if (bi1.length < bi2.length)
                {
                    flag = true;
                    x = bi2.data;
                    xMax = bi2.length;
                    y = bi1.data;
                    yMax = bi1.length;
                }
                else
                {
                    x = bi1.data;
                    xMax = bi1.length;
                    y = bi2.data;
                    yMax = bi2.length;
                }

                uint[] r = bi1.data;

                ulong sum = 0;

                // Add common parts of both numbers
                do
                {
                    sum += ((ulong)x[i]) + ((ulong)y[i]);
                    r[i] = (uint)sum;
                    sum >>= 32;
                } while (++i < yMax);

                // Copy remainder of longer number while carry propagation is required
                bool carry = (sum != 0);

                if (carry)
                {
                    if (i < xMax)
                    {
                        do
                            carry = ((r[i] = x[i] + 1) == 0);
                        while (++i < xMax && carry);
                    }

                    if (carry)
                    {
                        r[i] = 1;
                        bi1.length = ++i;
                        return;
                    }
                }

                // Copy the rest
                if (flag && i < xMax - 1)
                {
                    do
                        r[i] = x[i];
                    while (++i < xMax);
                }

                bi1.length = xMax + 1;
                bi1.Normalize();
            }

            #endregion Addition/Subtraction

            #region Compare

            /// <summary>
            /// Compares two BigInteger
            /// </summary>
            /// <param name="bi1">A BigInteger</param>
            /// <param name="bi2">A BigInteger</param>
            /// <returns>The sign of bi1 - bi2</returns>
            public static Sign Compare(BigInteger bi1, BigInteger bi2)
            {
                //
                // Step 1. Compare the lengths
                //
                uint l1 = bi1.length, l2 = bi2.length;

                while (l1 > 0 && bi1.data[l1 - 1] == 0) l1--;
                while (l2 > 0 && bi2.data[l2 - 1] == 0) l2--;

                if (l1 == 0 && l2 == 0) return Sign.Zero;

                // bi1 len < bi2 len
                if (l1 < l2) return Sign.Negative;
                // bi1 len > bi2 len
                else if (l1 > l2) return Sign.Positive;

                //
                // Step 2. Compare the bits
                //

                uint pos = l1 - 1;

                while (pos != 0 && bi1.data[pos] == bi2.data[pos]) pos--;

                if (bi1.data[pos] < bi2.data[pos])
                    return Sign.Negative;
                else if (bi1.data[pos] > bi2.data[pos])
                    return Sign.Positive;
                else
                    return Sign.Zero;
            }

            #endregion Compare

            #region Division

            #region Dword

            /// <summary>
            /// Performs n / d and n % d in one operation.
            /// </summary>
            /// <param name="n">A BigInteger, upon exit this will hold n / d</param>
            /// <param name="d">The divisor</param>
            /// <returns>n % d</returns>
            public static uint SingleByteDivideInPlace(BigInteger n, uint d)
            {
                ulong r = 0;
                uint i = n.length;

                while (i-- > 0)
                {
                    r <<= 32;
                    r |= n.data[i];
                    n.data[i] = (uint)(r / d);
                    r %= d;
                }
                n.Normalize();

                return (uint)r;
            }

            public static uint DwordMod(BigInteger n, uint d)
            {
                ulong r = 0;
                uint i = n.length;

                while (i-- > 0)
                {
                    r <<= 32;
                    r |= n.data[i];
                    r %= d;
                }

                return (uint)r;
            }

            public static BigInteger DwordDiv(BigInteger n, uint d)
            {
                BigInteger ret = new BigInteger(Sign.Positive, n.length);

                ulong r = 0;
                uint i = n.length;

                while (i-- > 0)
                {
                    r <<= 32;
                    r |= n.data[i];
                    ret.data[i] = (uint)(r / d);
                    r %= d;
                }
                ret.Normalize();

                return ret;
            }

            public static BigInteger[] DwordDivMod(BigInteger n, uint d)
            {
                BigInteger ret = new BigInteger(Sign.Positive, n.length);

                ulong r = 0;
                uint i = n.length;

                while (i-- > 0)
                {
                    r <<= 32;
                    r |= n.data[i];
                    ret.data[i] = (uint)(r / d);
                    r %= d;
                }
                ret.Normalize();

                BigInteger rem = (uint)r;

                return new BigInteger[] { ret, rem };
            }

            #endregion Dword

            #region BigNum

            public static BigInteger[] multiByteDivide(BigInteger bi1, BigInteger bi2)
            {
                if (Kernel.Compare(bi1, bi2) == Sign.Negative)
                    return new BigInteger[2] { 0, new BigInteger(bi1) };

                bi1.Normalize(); bi2.Normalize();

                if (bi2.length == 1)
                    return DwordDivMod(bi1, bi2.data[0]);

                uint remainderLen = bi1.length + 1;
                int divisorLen = (int)bi2.length + 1;

                uint mask = 0x80000000;
                uint val = bi2.data[bi2.length - 1];
                int shift = 0;
                int resultPos = (int)bi1.length - (int)bi2.length;

                while (mask != 0 && (val & mask) == 0)
                {
                    shift++; mask >>= 1;
                }

                BigInteger quot = new BigInteger(Sign.Positive, bi1.length - bi2.length + 1);
                BigInteger rem = (bi1 << shift);

                uint[] remainder = rem.data;

                bi2 = bi2 << shift;

                int j = (int)(remainderLen - bi2.length);
                int pos = (int)remainderLen - 1;

                uint firstDivisorByte = bi2.data[bi2.length - 1];
                ulong secondDivisorByte = bi2.data[bi2.length - 2];

                while (j > 0)
                {
                    ulong dividend = ((ulong)remainder[pos] << 32) + (ulong)remainder[pos - 1];

                    ulong q_hat = dividend / (ulong)firstDivisorByte;
                    ulong r_hat = dividend % (ulong)firstDivisorByte;

                    do
                    {
                        if (q_hat == 0x100000000 ||
                            (q_hat * secondDivisorByte) > ((r_hat << 32) + remainder[pos - 2]))
                        {
                            q_hat--;
                            r_hat += (ulong)firstDivisorByte;

                            if (r_hat < 0x100000000)
                                continue;
                        }
                        break;
                    } while (true);

                    //
                    // At this point, q_hat is either exact, or one too large
                    // (more likely to be exact) so, we attempt to multiply the
                    // divisor by q_hat, if we get a borrow, we just subtract
                    // one from q_hat and add the divisor back.
                    //

                    uint t;
                    uint dPos = 0;
                    int nPos = pos - divisorLen + 1;
                    ulong mc = 0;
                    uint uint_q_hat = (uint)q_hat;
                    do
                    {
                        mc += (ulong)bi2.data[dPos] * (ulong)uint_q_hat;
                        t = remainder[nPos];
                        remainder[nPos] -= (uint)mc;
                        mc >>= 32;
                        if (remainder[nPos] > t) mc++;
                        dPos++; nPos++;
                    } while (dPos < divisorLen);

                    nPos = pos - divisorLen + 1;
                    dPos = 0;

                    // Overestimate
                    if (mc != 0)
                    {
                        uint_q_hat--;
                        ulong sum = 0;

                        do
                        {
                            sum = ((ulong)remainder[nPos]) + ((ulong)bi2.data[dPos]) + sum;
                            remainder[nPos] = (uint)sum;
                            sum >>= 32;
                            dPos++; nPos++;
                        } while (dPos < divisorLen);
                    }

                    quot.data[resultPos--] = (uint)uint_q_hat;

                    pos--;
                    j--;
                }

                quot.Normalize();
                rem.Normalize();
                BigInteger[] ret = new BigInteger[2] { quot, rem };

                if (shift != 0)
                    ret[1] >>= shift;

                return ret;
            }

            #endregion BigNum

            #endregion Division

            #region Shift

            public static BigInteger LeftShift(BigInteger bi, int n)
            {
                if (n == 0) return new BigInteger(bi, bi.length + 1);

                int w = n >> 5;
                n &= ((1 << 5) - 1);

                BigInteger ret = new BigInteger(Sign.Positive, bi.length + 1 + (uint)w);

                uint i = 0, l = bi.length;
                if (n != 0)
                {
                    uint x, carry = 0;
                    while (i < l)
                    {
                        x = bi.data[i];
                        ret.data[i + w] = (x << n) | carry;
                        carry = x >> (32 - n);
                        i++;
                    }
                    ret.data[i + w] = carry;
                }
                else
                {
                    while (i < l)
                    {
                        ret.data[i + w] = bi.data[i];
                        i++;
                    }
                }

                ret.Normalize();
                return ret;
            }

            public static BigInteger RightShift(BigInteger bi, int n)
            {
                if (n == 0) return new BigInteger(bi);

                int w = n >> 5;
                int s = n & ((1 << 5) - 1);

                BigInteger ret = new BigInteger(Sign.Positive, bi.length - (uint)w + 1);
                uint l = (uint)ret.data.Length - 1;

                if (s != 0)
                {
                    uint x, carry = 0;

                    while (l-- > 0)
                    {
                        x = bi.data[l + w];
                        ret.data[l] = (x >> n) | carry;
                        carry = x << (32 - n);
                    }
                }
                else
                {
                    while (l-- > 0)
                        ret.data[l] = bi.data[l + w];
                }
                ret.Normalize();
                return ret;
            }

            #endregion Shift

            #region Multiply

            public static BigInteger MultiplyByDword(BigInteger n, uint f)
            {
                BigInteger ret = new BigInteger(Sign.Positive, n.length + 1);

                uint i = 0;
                ulong c = 0;

                do
                {
                    c += (ulong)n.data[i] * (ulong)f;
                    ret.data[i] = (uint)c;
                    c >>= 32;
                } while (++i < n.length);
                ret.data[i] = (uint)c;
                ret.Normalize();
                return ret;
            }

            /// <summary>
            /// Multiplies the data in x [xOffset:xOffset+xLen] by
            /// y [yOffset:yOffset+yLen] and puts it into
            /// d [dOffset:dOffset+xLen+yLen].
            /// </summary>
            /// <remarks>
            /// This code is unsafe! It is the caller's responsibility to make
            /// sure that it is safe to access x [xOffset:xOffset+xLen],
            /// y [yOffset:yOffset+yLen], and d [dOffset:dOffset+xLen+yLen].
            /// </remarks>
            public static unsafe void Multiply(uint[] x, uint xOffset, uint xLen, uint[] y, uint yOffset, uint yLen, uint[] d, uint dOffset)
            {
                fixed (uint* xx = x, yy = y, dd = d)
                {
                    uint* xP = xx + xOffset,
                        xE = xP + xLen,
                        yB = yy + yOffset,
                        yE = yB + yLen,
                        dB = dd + dOffset;

                    for (; xP < xE; xP++, dB++)
                    {
                        if (*xP == 0) continue;

                        ulong mcarry = 0;

                        uint* dP = dB;
                        for (uint* yP = yB; yP < yE; yP++, dP++)
                        {
                            mcarry += ((ulong)*xP * (ulong)*yP) + (ulong)*dP;

                            *dP = (uint)mcarry;
                            mcarry >>= 32;
                        }

                        if (mcarry != 0)
                            *dP = (uint)mcarry;
                    }
                }
            }

            /// <summary>
            /// Multiplies the data in x [xOffset:xOffset+xLen] by
            /// y [yOffset:yOffset+yLen] and puts the low mod words into
            /// d [dOffset:dOffset+mod].
            /// </summary>
            /// <remarks>
            /// This code is unsafe! It is the caller's responsibility to make
            /// sure that it is safe to access x [xOffset:xOffset+xLen],
            /// y [yOffset:yOffset+yLen], and d [dOffset:dOffset+mod].
            /// </remarks>
            public static unsafe void MultiplyMod2p32pmod(uint[] x, int xOffset, int xLen, uint[] y, int yOffest, int yLen, uint[] d, int dOffset, int mod)
            {
                fixed (uint* xx = x, yy = y, dd = d)
                {
                    uint* xP = xx + xOffset,
                        xE = xP + xLen,
                        yB = yy + yOffest,
                        yE = yB + yLen,
                        dB = dd + dOffset,
                        dE = dB + mod;

                    for (; xP < xE; xP++, dB++)
                    {
                        if (*xP == 0) continue;

                        ulong mcarry = 0;
                        uint* dP = dB;
                        for (uint* yP = yB; yP < yE && dP < dE; yP++, dP++)
                        {
                            mcarry += ((ulong)*xP * (ulong)*yP) + (ulong)*dP;

                            *dP = (uint)mcarry;
                            mcarry >>= 32;
                        }

                        if (mcarry != 0 && dP < dE)
                            *dP = (uint)mcarry;
                    }
                }
            }

            public static unsafe void SquarePositive(BigInteger bi, ref uint[] wkSpace)
            {
                uint[] t = wkSpace;
                wkSpace = bi.data;
                uint[] d = bi.data;
                uint dl = bi.length;
                bi.data = t;

                fixed (uint* dd = d, tt = t)
                {
                    uint* ttE = tt + t.Length;
                    // Clear the dest
                    for (uint* ttt = tt; ttt < ttE; ttt++)
                        *ttt = 0;

                    uint* dP = dd, tP = tt;

                    for (uint i = 0; i < dl; i++, dP++)
                    {
                        if (*dP == 0)
                            continue;

                        ulong mcarry = 0;
                        uint bi1val = *dP;

                        uint* dP2 = dP + 1, tP2 = tP + 2 * i + 1;

                        for (uint j = i + 1; j < dl; j++, tP2++, dP2++)
                        {
                            // k = i + j
                            mcarry += ((ulong)bi1val * (ulong)*dP2) + *tP2;

                            *tP2 = (uint)mcarry;
                            mcarry >>= 32;
                        }

                        if (mcarry != 0)
                            *tP2 = (uint)mcarry;
                    }

                    // Double t. Inlined for speed.

                    tP = tt;

                    uint x, carry = 0;
                    while (tP < ttE)
                    {
                        x = *tP;
                        *tP = (x << 1) | carry;
                        carry = x >> (32 - 1);
                        tP++;
                    }
                    if (carry != 0) *tP = carry;

                    // Add in the diagnals

                    dP = dd;
                    tP = tt;
                    for (uint* dE = dP + dl; (dP < dE); dP++, tP++)
                    {
                        ulong val = (ulong)*dP * (ulong)*dP + *tP;
                        *tP = (uint)val;
                        val >>= 32;
                        *(++tP) += (uint)val;
                        if (*tP < (uint)val)
                        {
                            uint* tP3 = tP;
                            // Account for the first carry
                            (*++tP3)++;

                            // Keep adding until no carry
                            while ((*tP3++) == 0)
                                (*tP3)++;
                        }
                    }

                    bi.length <<= 1;

                    // Normalize length
                    while (tt[bi.length - 1] == 0 && bi.length > 1) bi.length--;
                }
            }

            /*
			 * Never called in BigInteger (and part of a private class)
			 * 			public static bool Double (uint [] u, int l)
						{
							uint x, carry = 0;
							uint i = 0;
							while (i < l) {
								x = u [i];
								u [i] = (x << 1) | carry;
								carry = x >> (32 - 1);
								i++;
							}
							if (carry != 0) u [l] = carry;
							return carry != 0;
						}*/

            #endregion Multiply

            #region Number Theory

            public static BigInteger gcd(BigInteger a, BigInteger b)
            {
                BigInteger x = a;
                BigInteger y = b;

                BigInteger g = y;

                while (x.length > 1)
                {
                    g = x;
                    x = y % x;
                    y = g;
                }
                if (x == 0) return g;

                // TODO: should we have something here if we can convert to long?

                //
                // Now we can just do it with single precision. I am using the binary gcd method,
                // as it should be faster.
                //

                uint yy = x.data[0];
                uint xx = y % yy;

                int t = 0;

                while (((xx | yy) & 1) == 0)
                {
                    xx >>= 1; yy >>= 1; t++;
                }
                while (xx != 0)
                {
                    while ((xx & 1) == 0) xx >>= 1;
                    while ((yy & 1) == 0) yy >>= 1;
                    if (xx >= yy)
                        xx = (xx - yy) >> 1;
                    else
                        yy = (yy - xx) >> 1;
                }

                return yy << t;
            }

            public static uint modInverse(BigInteger bi, uint modulus)
            {
                uint a = modulus, b = bi % modulus;
                uint p0 = 0, p1 = 1;

                while (b != 0)
                {
                    if (b == 1)
                        return p1;
                    p0 += (a / b) * p1;
                    a %= b;

                    if (a == 0)
                        break;
                    if (a == 1)
                        return modulus - p0;

                    p1 += (b / a) * p0;
                    b %= a;
                }
                return 0;
            }

            public static BigInteger modInverse(BigInteger bi, BigInteger modulus)
            {
                if (modulus.length == 1) return modInverse(bi, modulus.data[0]);

                BigInteger[] p = { 0, 1 };
                BigInteger[] q = new BigInteger[2];    // quotients
                BigInteger[] r = { 0, 0 };             // remainders

                int step = 0;

                BigInteger a = modulus;
                BigInteger b = bi;

                ModulusRing mr = new ModulusRing(modulus);

                while (b != 0)
                {
                    if (step > 1)
                    {
                        BigInteger pval = mr.Difference(p[0], p[1] * q[0]);
                        p[0] = p[1]; p[1] = pval;
                    }

                    BigInteger[] divret = multiByteDivide(a, b);

                    q[0] = q[1]; q[1] = divret[0];
                    r[0] = r[1]; r[1] = divret[1];
                    a = b;
                    b = divret[1];

                    step++;
                }

                if (r[0] != 1)
                    throw (new ArithmeticException("No inverse!"));

                return mr.Difference(p[0], p[1] * q[0]);
            }

            #endregion Number Theory
        }
    }
}